The invention relates to a multi-layered plastic container, produced by coextrusion blow-molding with web-shaped designed pinch seam.
Multi-layered plastic containers produced by coextrusion blow-molding are being increasingly used, since the multiplicity of layers allows the positive properties of various plastics to be combined. The container wall can consequently be provided with properties which either cannot be achieved with one raw material alone, or which would cause high material costs if a single raw material suitable in itself were to be used solely by itself.
Multi-layered containers are required for improving the barrier properties of the container wall to gases and vapors, which can be achieved by the application of a barrier layer without the deformation behavior or the stress-cracking resistance of the base material. As the barrier layer often consists of a material of a different type than that of the base material, a bonding agent layer is arranged between base material and barrier layer. For better mechanical protection, the barrier layer is often arranged between two base layers. For example a container wall built up in this way, looks as follows: Base layer (polyolefine) - bonding agent - barrier layer (polyamide) - bonding agent - base layer (polyolefine), the layer thickness of the barrier layers and bonding agent layers being small in comparison with the base layers. Extrusion blow-molding is well know per se. Further details concerning plastics which can be used and equipment details can be obtained for example from the two books "Extrusionsblasformen" (Extrusion Blow-Molding), publisher: Verein DE Ingenieure, VDI-Ges. Kunststoff-technik - VDI-Verlag Dusseldorf, 1979 and "Technologien des Blasformens", (Blow-Molding Techniques) which appeared in 1977 from the same publisher in the same publishing house.
When forming the neck and bottom pinch seams during the course of container production, a weakening of the wall occurs at these points. The base layer on the inside bonds in the accustomed way, but the barrier layer and base layer on the outside are virtually only severed. A force acting on the pinch seam consequently has to be absorbed by the base layer on the inside alone. As the barrier layers are not welded to each other, an increased diffusion also occurs in the same region.
Therefore, containers have become known wherein, to improve strength, the point of joining is made as a web seam protruding from the container. However, for reasons of appearance or space, often such a web seam cannot be used or not with a sufficient height, and furthermore its strength is also inadequate. This is often true in the case of sizeable containers.
An object of the invention is to provide a container on which the durability of the seam is substantially improved.
This object is achieved in the case of a container of the above-noted type by folding the web seam in labyrinthal or meandering shape with the folds of the web seam being welded to each other and positively interlocking in the direction to resist bursting forces from within. Here the length of the web seam in the unfolded state is equivalent to at least three times the thickness of the coextrudate, and wherein the web seam is folded at least doubly.
In the production of containers by blow-molding, the seam (pinch seam) is designed as a web, which is folded in labyrinthal or meandering shape and the folds are welded to each other. Good strengths are achieved if the web weld is folded at least doubly. Multiple folding with many more folds generally does not bring any improvement in the seam strength. It is, favorable if the length of the web seam in the unfolded state is at least three times the thickness of the coextrudate, i.e., is equivalent to the wall thickness of the container in the region of the welding point. It is particularly favorable if, as well as the welding, the folding achieve a positive bonding of the extrudite.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.